1. Field of the Invention
The present invention relates generally to drilling a subterranean borehole and, more specifically, drilling structures disposed on the end of a casing or liner.
2. State of the Art
The drilling of wells for oil and gas production conventionally employs longitudinally extending sections or so-called “strings” of drill pipe to which, at one end, is secured a drill bit of a larger diameter. After a selected portion of the borehole has been drilled, the borehole is usually lined or cased with a string or section of casing. Such a casing or liner usually exhibits a larger diameter than the drill pipe and a smaller diameter than the drill bit. Therefore, drilling and casing according to the conventional process typically require sequentially drilling the borehole using a drill string with a drill bit attached thereto, removing the drill string and drill bit from the borehole, and disposing casing into the borehole. Further, often after a section of the borehole is lined with casing, which is usually cemented into place, additional drilling beyond the end of the casing may be desired.
However, sequential drilling and casing may be time consuming and costly because at the considerable depths the time required to implement complex retrieval procedures to recover the drill string may be lengthy.